The present invention relates to a motor with an electromagnetic brake that prevents a shaft from rotating together with a load when the motor is not driven.
Japanese Patent Publication No. 2005-124259 (JP2005-124259A), for example, discloses a motor including a motor stator and a motor rotor that includes a shaft formed of a ferromagnetic material and rotates relative to the motor stator. Then, the motor is provided with an electromagnetic brake in order to prevent the shaft from rotating together with a load at a time of emergency stop. The electromagnetic brake includes a brake friction plate fixed to the shaft, a brake plate, and an electromagnetic coil disposed on a brake core. When braking is applied, the electromagnetic brake brings the brake plate into contact with the brake friction plate, thereby preventing the shaft from rotating. When braking is not applied, the electromagnetic brake keeps the brake plate and the brake friction plate apart from each other by means of an electromagnetic force generated by the electromagnetic coil, thereby allowing the shaft to rotate. In the motor of this type, however, a magnetic sensor is usually disposed outside an end of a non-load-side end portion of the shaft. Thus, leakage magnetic flux that has been generated by the electromagnetic coil and leaked through the shaft may pass through the magnetic sensor. Malfunction of the magnetic sensor may thereby occur. Then, JP2005-124259A proposes the following. An internal fan that discharges heat inside the motor to outside is provided at a portion of the shaft closer to the non-load-side end portion than the electromagnetic brake. Then, a heat shielding plate is provided at a bracket. The brake core, with the electromagnetic coil disposed thereon, is fixed to the bracket. Then, each of the internal fan and heat shielding plate is formed of a ferromagnetic material. With this arrangement, a portion of the leakage magnetic flux that has been generated by the electromagnetic coil and leaked through the shaft is guided back to the electromagnetic coil through the internal fan and the heat shielding plate. Reduction of influence of the leakage magnetic flux on the magnetic sensor is thereby planned.
However, in the motor with an electromagnetic brake disclosed in JP2005-124259A, the bracket at which the heat shielding plate is provided is formed of aluminum, which is a nonmagnetic material. Further, the leakage magnetic flux cannot be flown from the internal fan to the heat shielding plate. Accordingly, the influence of the leakage magnetic flux on the magnetic sensor cannot effectively be reduced.
The overall shaft or the non-load-side end portion of the shaft may be formed of a nonmagnetic material such as stainless steel. In this configuration, however, it becomes difficult to process the shaft, and material cost for the shaft is also increased.